keV Protons Research Articles

Quantifying the Effect of Magnetic Field Line Curvature Scattering on the Loss of Ring Current Ions

AbstractDuring geomagnetic storms, the ring current ions sometimes exhibit rapid loss as suggested by the fast recovery of the Dst index on a time scale of a few hours. The effects of magnetic field line curvature (FLC) scattering on the loss of ring current ions, which have not been well quantified, are studied here by test particle simulations under the T89c magnetic field model. Our simulation results show that the prediction of ion loss based on a single‐value cutoff of the κ parameter or maximum of of a single FLC scattering is not accurate. Instead, the e‐folding lifetime (τ) for the loss of ring current ions due to cumulative FLC scattering has been calculated for different initial ion energies, equatorial pitch angles, and L shells under different geomagnetic conditions. The results show that in general the FLC scattering loss is faster for ions of higher energy, higher mass, smaller pitch angle, higher L, and at high Kp level. Specifically, we find that at Kp = 6 the lifetime can be <10 h at L > 5 for 100 s keV protons and at L > 4 for 100 s keV O+, which demonstrates that FLC scattering can be an important mechanism for the observed fast loss (τ < 10 h) of ring current ions during geomagnetic storms. Furthermore, we formulate an empirical formula for τ as a function of ion energy, pitch angle, position, species, and Kp. The empirical formula can be directly included in ring current models to account for the FLC scattering effects.

Complex Sub‐Auroral Flow Channel Structure Formed by Double‐Peak Sub‐Auroral Ion Drifts (DSAID) and Abnormal Sub‐Auroral Ion Drifts (ASAID)

AbstractBy utilizing multi‐instrument and multi‐satellite/spacecraft observations, we report the repeated development of a temporary and complex sub‐auroral flow channel (FC) structure during the intensive storms investigated. Appearing as combined double‐peak sub‐auroral ion drifts (DSAID) and abnormal SAID (ASAID), it is called DSAID‐ASAID FC structure. Revealing its development, various other FCs and features appeared in the auroral and polar regions simultaneously. These include the auroral Harang Region (HR) that is the Substorm Current Wedge's ionospheric signature and the Eastward FC (E‐FC) indicating the arrival of the Westward Travelling Surge. Results show that in the HR and E‐FC, the locally enhanced duskside upward Region 1 Field Aligned Currents (↑R1 FACs) connected in the magnetosphere with the meridional partial ring current characterized by a double plasma density/pressure peak structure, of which signature was seen in the 225 keV proton density data, leading to the development of two sets of ↓R2 FACs and DSAID. Meanwhile, large auroral undulations appeared and were driven, via magnetosphere‐ionosphere coupling, by Kelvin‐Helmholtz instability mechanisms that also drove plasma sheet rippling leading to ASAID development. Plasma sheet rippling occurred during magnetotail reconnection, as demonstrated with its ionospheric polar cap signature, known as FC‐3, in a stretched tail region according to the b2i boundary located at ∼60° magnetic latitude. Then, the earthward flows' braking/slowing down provided the energy for driving the R1‐R2 FACs. From the observational evidence presented we conclude that the DSAID‐ASAID features investigated developed due to the maintenance of DSAID during plasma sheet rippling triggering ASAID development.

Conditions of Loss Cone Filling by Scattering on the Curved Field Lines for 30 keV Protons During Geomagnetic Storm as Inferred From Numerical Trajectory Tracing

AbstractThe rate of pitch angle scattering on the curved magnetic field lines is well parameterized by the ratio of the minimum field line curvature radius to the maximum effective particle gyroradius (K = RC/rg). The critical value of this ratio (Kcr) corresponding to the loss cone filling is of special interest since it corresponds to the low altitude isotropic boundaries (IBs). The early theoretical estimates gave Kcr = 8, whereas recent estimations of the K parameter on the field lines corresponding to the observed IBs during the geomagnetic storms revealed KIB values in the range of 3–30. We numerically trace the trajectories of the 30 keV protons in the magnetic field of the global magnetohydrodynamic simulation of the intense storm in order to infer statistical distribution of Kcr. The electric field and effects of nonstationarity are neglected in this study. It is found that although the Kcr values do show some variations during the course of the storm, its range is rather narrow 4 < Kcr < 8. The result suggests that higher KIB values found in the observational studies, if not caused by the magnetosphere‐ionosphere mapping error, should be attributed to some other mechanism of pitch angle scattering. The Kcr values tend to be lower (4–6) during the main phase because the region of low K values approaches the Earth and the equatorial loss cone size becomes larger due to a larger equatorial magnetic field in the near‐earth region. The remaining variation of Kcr is explained by the presence of the guide component of the magnetic field.

In-air proton beam irradiation induced radiolysis of methyl orange in aqueous solution

Proton irradiation induced radiolysis of methyl orange was investigated in aqueous solution with an in-air ion beam setup. 566–3024 keV energy protons were used for the irradiations of 1.6 mM aqueous methyl orange solutions, in the presence and absence of tert-butanol radical scavenger. The decoloration of methyl orange was followed by UV/vis spectrophotometry. It was found that the methyl orange can be efficiently decolorized in the applied energy range, caused by degradation processes. Furthermore, the efficiency of methyl orange radiolysis was found to be dependent on the applied proton energy. The irradiations were also carried out in the presence of 0.16 and 0.73 mol dm−3 tert-butanol using 3024 keV protons. It was found, that at lower concentration of radical scavenger the degradation was less efficient, while at higher concentration of the radical scavenger, interestingly, the degradation was more efficient when compared to the scavenger-less irradiation experiments. Initial G-values were determined for all ion energies and for different scavenger concentrations.

Er3+/Yb3+ co-doped phosphate glass waveguides formed by the H+ ion implantation

The 400 keV proton implantation with a fluence of [Formula: see text] ions/cm2 was applied on the [Formula: see text] co-doped phosphate glass to fabricate a planar waveguide structure. The mode profile at the end face of the waveguide was measured by the end-face coupling technique. The energy loss profile of the energetic protons was calculated by the SRIM 2013. The refractive index distribution was simulated by the reflectivity calculation method. Based on these results, the formation theory of the planar waveguides was discussed through simulating the energy loss distribution and analyzing the reconstructed refractive index profile, which could be used for applications in the future integrated optical systems.

Study on the Microstructure of Polyether Ether Ketone Films Irradiated with 170 keV Protons by Grazing Incidence Small Angle X-ray Scattering (GISAXS) Technology

Polyether ether ketone (PEEK) films irradiated with 170 keV protons were calculated by the stopping and ranges of ions in matter (SRIM) software. The results showed that the damage caused by 170 keV protons was only several microns of the PEEK surface, and the ionization absorbed dose and displacement absorbed dose were calculated. The surface morphology and roughness of PEEK after proton irradiation were studied by atomic force microscope (AFM). GISAXS was used to analyze the surface structural information of the pristine and irradiated PEEK. The experimental results showed that near the surface of the pristine and irradiated PEEK exists a peak, and the peak gradually disappeared with the increasing of the angles of incidence and the peak changed after irradiation, which implies the 170 keV protons have an effect on PEEK structure. The influences of PEEK irradiated with protons on the melting temperature and crystallization temperature was investigated by differential scanning calorimetry (DSC). The DSC results showed that the crystallinity of the polymer after irradiation decreased. The structure and content of free radicals of pristine and irradiated PEEK were studied by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The stress and strain test results showed that the yield strength of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 was higher than the pristine, but the elongation at break of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 decreased obviously.

Response of structural and optical properties against proton irradiation in AlN:Tm thin films

Thulium (Tm) doped aluminum nitride (AlN) thin films are deposited by radio frequency (RF) magnetron sputtering in a pure nitrogen atmosphere. As-deposited thin films are irradiated at room temperature with 335 keV protons and a fluence of 1 × 1014 ions/cm2. The effects of irradiation on the structural and optical properties of the deposited thin films are investigated. Rutherford backscattering (RBS) is performed to determine the thickness and stoichiometric properties of the films while the structural properties of the material before and after irradiation are investigated with x-ray diffraction (XRD). Non-ionizing energy loss (NIEL) study demonstrates that scattering events increase as the ions penetrate deep into the matrix and result in higher damage in the material. Fourier transform infrared spectroscopy (FTIR) is used to see the absorption spectra of thin films which reveals that the implanted films have great capabilities of solar energy storage. Bandgap of the film is determined using diffused reflection spectroscopy (DRS) technique, where a slight upwards shift in bandgap is observed due to irradiation induced material damages.

Prediction and Understanding of Soft-proton Contamination in XMM-Newton: A Machine Learning Approach

Abstract One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes are few tens to hundreds of keV (soft) protons concentrated by the mirrors. One such telescope is the European Space Agency’s (ESA) X-ray Multi-Mirror Mission (XMM-Newton). Its observing time lost due to background contamination is about 40%. This loss of observing time affects all the major broad science goals of this observatory, ranging from cosmology to astrophysics of neutron stars and black holes. The soft-proton background could dramatically impact future large X-ray missions such as the ESA planned Athena mission (http://www.the-athena-x-ray-observatory.eu/). Physical processes that trigger this background are still poorly understood. We use a machine learning (ML) approach to delineate related important parameters and to develop a model to predict the background contamination using 12 yr of XMM-Newton observations. As predictors we use the location of the satellite and solar and geomagnetic activity parameters. We revealed that the contamination is most strongly related to the distance in the southern direction, Z (XMM-Newton observations were in the southern hemisphere), the solar wind radial velocity, and the location on the magnetospheric magnetic field lines. We derived simple empirical models for the first two individual predictors and an ML model that utilizes an ensemble of the predictors (Extra-Trees Regressor) and gives better performance. Based on our analysis, future missions should minimize observations during times associated with high solar wind speed and avoid closed magnetic field lines, especially at the dusk flank region in the southern hemisphere.

Radiation Induced Defects in Hollow Particles of Zinc Oxide

Radiation stability of ZnO hollow particles under 100 keV proton and electron exposure have been investigated. The experimental data were compared with the calculated ones obtained by modeling in the GEANT4 software package. Hollow particles have better radiation stability compared with bulk microparticles cause by low defects accumulation in the hollow particles, which was confirmed by simulation in GEANT4.

Absolute measurements of the double differential electronic emission cross-sections of isolated pyrene molecule (C16H10) in interaction with keV protons

Electronic emission of an isolated pyrene molecule induced by 50 to 125 keV protons has been investigated. The corresponding absolute double differential cross-sections have been measured at an angle of 35° with respect to the incident proton beam axis. These measurements were compared to the simulations of emitted electrons’ spectra using a semi-classical trajectory Monte-Carlo (SCTMC) approach. The simulated SCTMC cross-sections show reasonably good agreement with the measured ones.

Pre-equilibrium stopping and charge capture in proton-irradiated aluminum sheets

We present a first-principles study of pre-equilibrium stopping power and projectile charge capture in thin aluminum sheets irradiated by 6 - 60 keV protons. Our time-dependent density functional theory calculations reveal enhanced stopping power compared to bulk aluminum, particularly near the entrance layers. We propose the additional excitation channel of surface plasma oscillations as the most plausible explanation for this behavior. We also introduce a novel technique to compute the orbital-resolved charge state of a proton projectile after transmission through the sheet. Our results provide insight into the dynamics of orbital occupations after the projectile exits the aluminum sheet and have important implications for advancing radiation hardness and focused-ion beam techniques, especially for few-layer materials.

Ejected-electron-energy and angular dependence of fully differential ionization cross sections in medium-velocity proton collisions with He and H2

We have measured fully momentum-analyzed recoiling target ions and scattered projectiles, produced in ionization of He and ${\mathrm{H}}_{2}$ by 75 keV proton impact, in coincidence. The momentum of the ejected electrons was deduced from momentum conservation. From the data we extracted fully differential ionization cross sections as a function of the polar electron emission angle (for fixed electron energies) and as a function of the electron energy (for fixed electron emission angles). Comparison between experiment and various distorted wave calculations confirms that under kinematic conditions where the post-collision interaction plays an important role, the few-body dynamics underlying the ionization process are still poorly understood.

The influence of radiation damage on electrons and ion scattering measurements from PVC films

Polyvinyl chloride (PVC) is a material that decomposes rapidly when irradiated by charged particles. Here we use energy spectra of electrons reflected from the PVC films during electron radiation to monitor this process. This is accomplished by measuring the energy distribution of elastically scattered electrons which depends on the mass of the scattering atoms. Incoming electrons with energy between 5 and 40 keV are used. Information is obtained about both the relative amount of Cl, C and H present in the sample. Especially the Cl concentration decreases quickly during irradiation. At larger energy losses the signature of the band gap is visible in the energy loss spectrum. The number of excitations within the band gap increases rapidly when the composition of the film changes. The H intensity is somewhat less affected by the electron beam than the Cl intensity but accurate determination of the H content is complicated due to the changing background. Medium-energy ion scattering measurements (using 200 keV protons) and Rutherford backscattering measurements (using 2 MeV He ions) showed a strong decrease in the measured Cl intensity with ion fluence used. The Cl concentration as a function of fluence for electrons, protons and He ions can be described in a uniform way by considering the density of electronic excitations produced under the different irradiation conditions.

Double differential cross sections for ionization of H by 75 keV proton impact: Assessing the role of correlated wave functions* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11974229 and 11274215).

The effect of final-state dynamic correlation is investigated for ionization of atomic hydrogen by 75-keV proton impact by analyzing double differential cross sections. The final state is represented by a continuum correlated wave (CCW-PT) function which accounts for the interaction between the projectile and the target nucleus (PT interaction). The correlated final state is nonseparable solutions of the wave equation combining the dynamics of the electron motion relative to the target and projectile, satisfying the Redmond’s asymptotic conditions corresponding to long range interactions. The transition matrix is evaluated using the CCW-PT function and the undistorted initial state. Both the correlation effects and the PT interaction are analyzed by the present calculations. The convergence of the continuous correlated final state is examined carefully. Our results are compared with the absolute experimental data measured by Laforge et al. [Phys. Rev. Lett. 103, 053201 (2009)] and Schulz et al. [Phys. Rev. A 81, 052705 (2010)], as well as other theoretical models (especially the results of the latest non perturbation theory). We have shown that the dynamic correlation plays an important role in the ionization of atomic hydrogen by proton impact. While overall agreement between theory and the experimental data is encouraging, detailed agreement is still lacking. However, such an analysis is meaningful because it provides valuable information about the dynamical correlation and PT interaction in the CCW-PT theoretical model.

Can Solar Wind Decompressive Discontinuities Suppress Magnetospheric Electromagnetic Ion Cyclotron Waves Associated With Fresh Proton Injections?

AbstractElectromagnetic ion cyclotron (EMIC) waves play an important role in the energy transfer among particles of different energies and species in the magnetosphere, whose drivers have been commonly recognized as solar wind compressions and storm/substorm proton injections. However, how the solar wind decompressions related to frequently occurring discontinuities compete with the proton injections in the evolution of EMIC waves has been rarely investigated. Here we present a complete end‐to‐end observation by Wind, THEMIS, and Van Allen Probes missions during the main phase of the 23 February 2014 storm of a succession of solar wind rotational discontinuities decompressing the magnetosphere within 200 s, adiabatically decelerating the freshly injected >10 keV protons, and thus suppressing the EMIC waves in the inner magnetosphere. Our results highlight the importance of solar wind conditions for the evolution of inner magnetospheric EMIC waves from a new perspective.

Effects of Polarization Reversal on the Pitch Angle Scattering of Radiation Belt Electrons and Ring Current Protons by EMIC Waves

AbstractIn this study, we investigate the effects of polarization reversal of electromagnetic ion cyclotron (EMIC) waves at the crossover frequencies on computations of bounce‐averaged pitch angle diffusion coefficients of radiation belt electrons and ring current protons. We find that inclusion of polarization reversal can cause significant changes of H+ band‐induced particle diffusion coefficients, while scattering by the He+ band is almost unaffected. Our results show that the pure L‐mode approach, which has been widely implemented in previous studies, tends to underestimate the diffusion coefficients of ultrarelativistic (>4 MeV) electrons and overestimate those of 10–50 and >100 keV protons caused by H+ band EMIC waves. Especially for >100 keV protons, the differences in diffusion coefficients can be larger by an order of magnitude. We confirm that the polarization reversal can contribute importantly to the scattering loss of radiation belt electrons and ring current protons by H+ band EMIC waves.

Taper angle dependence of the dynamical transmission of several-hundred-keV protons through PC conical capillary

The dynamical transmission of intermediate-energy protons through a polycarbonate (PC) conical capillary with taper angle from 0.48° to 2° are simulated. The results show that for small taper angle of 0.48°, the transmission of 100 keV protons is dominated by the deposited-charge-assisted specular reflection. This reflection effect decreases with the increase of the taper angle. When the taper angle is increased to 2°, the transmission of the protons is mainly influenced by small angle scattering, which is consistent with the experimental data. The asymptotic transmission rate decreases with the increase of the capillary taper angle. These results suggest that the deposited-charge-assisted specular reflection is significant in focusing several-hundred-keV protons.

Charge state distribution and energy loss for 100 keV protons moving in discharge H plasmas

Ab initio theoretical simulations are performed for charge state distribution and energy loss of a 100 keV proton beam propagating in partially ionized discharge H plasmas. In the simulation, all transition processes are calculated accurately among eight main projectile electronic configurations including the most relevant excited states. Projectile configuration evolution is computed by solving rate equations, and the effective charge state Zeff is obtained during all discharge stages. A new way is suggested to get the projectile energy loss with the contributions of all configurations considered separately. Such obtained energy losses are in the best agreement with experimental measurements among all the related models. However, both traditional empirical models with estimated Zeff and the standard stopping model are found invalid in this case, and relevant reasons are explored. Projectile capture and ionization processes in plasmas are found to be especially important in the stopping process. We predict that projectile excited states would make a much larger difference in energy deposition when a higher atomic number projectile is chosen, which has not been deeply recognized in plasmas yet.

Recovery and accumulation of ion irradiation damage leading to dose rate dependence in GaAs

Competing dynamics was analyzed for generation, recovery and accumulation of ion irradiation damage using three methods including He-ion channeling backscattering. The in situ tracing of electrical conductance after pulsed 100 keV proton irradiations at 23 °C–92 °C revealed that the subsequent recovery process was a second-order reaction with an activation energy of 0.74 eV in n-type and 0.31 eV in p-type epitaxial layers arising from long-range migration of both Ga and As interstitials. The amorphized depth by pulsed irradiations exhibited that the recovery was suppressed by the incidence of two ions within a lateral separation, which increased from ∼5 to ∼20 nm with the ion mass for 80 keV Ne+, 150 keV Ar+, and 300 keV Kr+ ions of an identical projected range, 115 nm. From the comparison with ion-collision simulations, it was concluded that if two collision cascades overlap before the recovery, it enhances interstitial clustering while suppressing the annihilation and causes the dose rate dependence.

Proton capture resonant state ofO15at 7556 keV

The slowest reaction in the CNO cycle 14N(p, gamma)15O has been studied by populating the E^lab_p =278 keV (E^r_c.m.=259 keV) proton capture resonant state of ^{15}O at 7556 keV. The strength of the resonance has been determined from the experimental data. The level lifetime of the sub-threshold resonant state at Ex=6792 keV, as well as the lifetimes of the 5181 keV and 6172 keV states, have been measured using the Doppler shift attenuation method (DSAM). The structural properties of the nucleus ^{15}O, such as, the level energies, transition strengths, level lifetimes, and spectroscopic factors, have been calculated theoretically by using the large basis shell model, which agrees reasonably well with the present as well as the previous experimental data.